When President John Kennedy challenged America to put a man on the moon, Paul Fisher knew no existing pen could perform in the gravity free, freezing cold and boiling hot vacuum of space. . Thousands of experiments later, Fischer succeeded in creating the first reliable sealed and pressurized cartridge. In 1967, after 18 months of rigorous testing by NASA, the Space Pen was selected by the astronauts. The Fischer Space Pen cartridge is guaranteed to perform in temperatures from 30deg to 250deg F. It will write over grease, underwater, in zero gravity, and at any angle even upside down!. Its reliability means its the only pen you will ever need. Features an ultra hard tungsten carbide tip. Thrixotropic ink in a hermetically sealed, pressurized reservoir writes three times longer than an ordinary ball point. Sliding float separates ink from pressurized nitrogen gas. Black ink medium point.